Carbon materials have been used in the form of a catalyst support, an adsorbing agent, a releasing agent, an ink, a toner etc., and attract attention on the structure thereof in recent years due to advent of nanocarbon materials, such as carbon nanotube and carbon nanohorn, having a size of nanometers. The applications thereof have been intensively investigated, as shown in Patent Publication-1 (carbon nanohorn), Patent Publication-2 (DDS), Patent Publication-3 (solid lubricant), Patent Publication-4 (insertion of methane gas), Patent Publication-5 (adsorbing agent), Patent Publication-6 (methane-decomposing catalyst), Patent Publication-7 (catalyst support), and Non-Patent Literature-1.
The unique structure of the carbon nanotube and carbon nanohorn attracts attention as the catalyst support for industrial use, is used recently as a catalyst support for a steam reforming catalyst in a fuel cell or manufacture of hydrogen, and reported as an optimum catalyst support in Patent Publication-7 and Non-patent Literature-1.
It is known in the above applications, for example, that the performance and physical properties of the supported catalyst depends on the mean particulate size, distribution etc. of the supported metal as well as the properties of the support on which the metallic catalyst particulates are supported.
The water solubility, adsorption site, specific surface area, etc. of the support are also the main factors that have a significant influence on the catalyst supporting process and catalyst performance. The catalyst ability basically depends on the specific surface area of the catalyst, which depends on the particulate size. A smaller particulate size increases the specific surface area, thereby improving the catalyst ability. However, since the size of particulates supported on any catalyst support under the present circumstances is about 1.5 to 3.0 nm at the maximum, a further reduction in the particulate size is the most crucial issue in the view point of catalyst efficiency.
It is ordinary for the catalyst to be used after activation or stabilization by anneal etc. thereof succeeding to supporting thereof on the support. However, it is known that the catalyst ability is impaired by aggregation and coarsening of the catalyst, and thus the coarsening of catalyst particulates is also one of the issues.
In addition, it is also known that if the catalyst particulates on the support are likely to move thereon, the coarsening of particulate size occurs during the use thereof due to aggregation of metallic catalyst particulates caused by those processes. This degrades the catalyst characteristic after a long term use thereof, incurring a practical problem on the durability of a battery cell or a steam reforming catalyst.                Patent Publication-1: JP-2002-159851A        Patent Publication-2: JP-2005-343885A        Patent Publication-3: JP-2003-313571A        Patent Publication-4: JP-2004-16976A        Patent Publication-5: JP-2005-7241A        Patent Publication-6: JP-2003-146606A        Patent Publication-7: JP-2004-152489A        Non-Patent Literature-1: K. Murata et al. Carbon 44, 799 (2006)        Non-patent literature-2: T. Yoshitake, Y. Shimakawa, S. Kuroshima, H. Kimura, T. Ichihashi, Y. Kubo, D. Kasuya, K. Takahashi, F. Kokai, M. Yudasaka, S. Iijima: Physical 2002, B323, p 124.        